Method of spectrally sensitizing photographic silver halide



United States Patent 3,482,981 METHOD OF SPECTRALLY SENSITIZING PHOTO-GRAPHIC SILVER HALIDE Earl John Van Lare, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 8, 1966, Ser. No. 532,593 Int. Cl. G03c 1/10 U.S. Cl. 96106 14 Claims ABSTRACT OF THE DISCLOSURE Photographic silver halide emulsions are spectrally sensitized by protonating a sensitizing dye having the amidinium ion auxochromophore system, and adding the protonated dye to a liquid photographic silver halide emulsion which has a pH sufiiciently high to convert the dye to its colored, unprotonated form, to spectrally sensitize the silver halide. The protonated dye can be dispersed in a hydrophilic colloid and the dispersion of dye in hydrophilic colloid can subsequently be combined with a fluid silver halide emulsion, either the colloid or the emulsion having a pH sufficiently high to convert the dye to its unprotonated, colored form. The invention avoids introduction of organic solvent into photographic emulsions, and thereby eliminates defects in emulsion coatings which are caused by organic solvent.

This invention relates to improved methods for spectrally sensitizing photographic silver halide emulsions. It also relates to aqueous solutions of certain protonated spectral sensitizing dyes.

Spectral sensitizing dyes containing the amidinium ion auxochromophore system are substantially water insoluble. Most of these spectral sensitizing dyes have been incorporated in silver halide emulsions by dissolving them in organic solvent solutions. Relatively large amounts of organic solvents are generally required to dissolve these dyes. When dye solutions containing substantial quantities of organic solvent are added to silver halide emulsions, coating defects frequently occur in applying the emulsion to a support. The presence of organic solvent in the emulsion tends to cause bare spots in the emulsion coating. In addition, organic solvent solutions of such dyes cannot be stored in light without damaging the dye.

It, therefore, appears highly desirable to provide methods for spectrally sensitizing photographic emulsions with dyes having the amidinium ion auxochromophore system whereby organic solvents can be eleminated from the emulsion, and highly stable solutions of the dye may be employed.

One object of this invention is to provide improved methods for spectrally sensitizing photographic silver halide emulsions with dyes containing the amidinium ion auxochromophore system. Another object of this invention is to provide highly light-stable aqueous solutions of protonated spectral sensitizing dyes having the amidinium ion auxochromophore system. A further object of this invention is to provide a method for spectrally sensitizing photographic silver halide emulsions with dyes having the amidinium ion auxochromophore system which does not involve the use of organic solvents. Other objects of this invention will appear from the following disclosure and the appended claims.

In accordince with one embodiment of this invention, a method is provided for spectrally sensitizing photographic silver halide grains dispersed in an alkali permeable colloid which comprises protonating a spectral sen sitizing dye having the amidinium ion auxochromophore system, dissolving the protonated dye in an aqueous solution, and adding the solution of protonated dye to a dis- 3,482,981 Patented Dec. 9, 1969 persion of silver halide grains in the alkali permeable colloid, which dispersion has a pH sufliciently high to convert the protonated dye to its colored form. It has been found that this method of spectrally sensitizing silver halide dispersions substantially reduces or eliminates the addition of organic solvents to the system. Thus, coating defects caused by organic solvent are eliminated. The aqueous solutions of protonated dye have substantially greater stability to light than aqueous organic solvent solutions of the corresponding unprotonated dyes.

In another embodiment of this invention, photographic silver halide emulsions are spectrally sensitized by protonating a spectral sensitizing dye havingthe amidinium ion auxachromophore system, forming an aqueous solution of said protonated dye, adding said aqueous solution of protonated dye to a hydrophilic colloid, dispersing said dye in said colloid; and then adding said dispersion of dye in colloid to a fluid photographic silver halide emulsion to spectrally sensitize said silver halide, the pH of at least one of said hydrophilic colloid and said silver halide emulsion being sufficiently high to convert the dye to its protonated form.

The invention also provides novel aqueous solutions of protonated photographic spectral sensitizing dyes containing the amidinium ion auxochromophore system. These solutions, as noted above, exhibit superior stability to light.

As used herein and in the appended claims, amidinium ion auxochromophore system is used broadly as in Mees, The Theory of the Photographic Process published in 1954 by Macmillan Company, pages 373, 375 and 376. The characteristic amidinium ion auxochromophore system is described below:

In the protonated form, the characteristic general formula may be written as follows:

In the above formulas, n can be 0 or an integer of from 1 to 4. (cf. Mees, p. 273.) The term protonated as used herein and in the appended claim refers to dyes having the general formula given immediately above. Dyes containing the amidinium ion auxochromophore system include the cyanine dyes and the hemicyanine dyes (including styryl dyes) which are photographic spectral sensitizers. Preferably, dyes containing the amidinium ion auxochromophore system are employed which, in the protonated form thereof, are soluble in water in the absence of any organic solvent. However, organic solvent may be added to dissolve certain dyes which, even in their protonated form, are difiicultly soluble in water. In other words, organic solvent may be added, preferably in relatively small quantities, to obtain more concentrated solutions of the dye if desired. The most useful dyes are those which can be protonated at a pH of over 1, e.g., pH 1 to 4.

Typical useful cyanine dyes Which may be protonated and employed in accordance with this invention have the following general formula:

ring, e.g., thiazole, 4-phenylthiazole, 4,5-diphenylthiazole, 4 (2 thienyDthiazole, 4-methylthiazole, benzothiazole, 4-chlorobenzothiazole, 4-methylbenzothiazole, 4-methoxybenzothiazole, 4-ethoxybenzothiazole, 4-phenylbenzothiazole, 5 ehlorobenzothiazole, 5 bromobenzothiazole, 5- methyl-benzothiazole, S-rnethoxybenzothiazole, S-ethoxybenzothiazole, S-phenylbenzothiazole, 6-chlorobenzothiazole, 6 bromobenzothiazole, 6 methylbenzothiazole, 6- rnethoxybenzothiazole, 6-ethoxybenzothiazole, 4-phenyloxazole, benzoxazole, S-chlorobenzoxazole, S-methylbenzoxazole, S-bromobenzoxazole, S-methoxybenzoxazole, 5- ethoxybenzoxazole, S-phenylbenzoxazole, l-alkyl imidazoles, l-aryl imidazoles, l-alkyl benzimidazoles, l-aryl benzimidazoles, S-chloro-l-alkyl benzimidazoles, S-chlorol-aryl benzimidazoles, 56 dichloro 1 alkyl benzimidazoles, 5,6-dichloro-1-aryl benzimidazoles, S-methoxy 1- alkyl benzimidazoles, S-methoxy-l-aryl benzimidazoles, 5-cyano-l-alkyl benzimidazoles, S-cyano-l-aryl benzimidazoles, 1-alky1naphth[l,2-d]imidazole, l arylnaphth[l,2- d]imidazole., 4 methylselenazole, 4 phenylselenazole, selenazole, benzoselenazole, S-chlorobenzoselenazel, wnaphthothiazole, fl-naphthothiazole, quinoline, 6-methylquinoline, 6-methoxyquinoline, 6-ethoxyquinoline, 6-chloroquinoline, 4-methoxyquinoline, 4-methylquinoline, 8- methoxyquinoline, B-rnethylquinoline, 4-chloroquinoline, 3,3-dimethylindlenine, etc.; X represents an acid anion, such as chloride, bromide, p-toluene sulfonate, methane sulfonate, methylsulfate, et-hylsulfate, perchlorate, etc.; R and R each represents an alcohol radical, e.g., an alkyl substituent (including substituted alkyl) having from 1 to 18, and preferably 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, hexyl, dodecyl, octadecyl, benzyl, beta-phenylethyl, sulfoalkyl such as ,fi-sulfoethyl, -sulfopropyl, 'y-sulfobutyl, 6-sulf0- butyl etc.; carboxyalkyl such as fl-carboxyethyl, 'y-carboxypropyl,6-carboxylbutyl etc. sulfatoalkyl such as 'y-sulfatopropyl and fi-sulfatobutyl, etc. It will be noted that in some instances, the acid anion, represented by X in the above formula, is included in the substituent represented by R such as dyes containing the betaine type structure. Some specific cyanine dyes that can be protonated and used in the process of this invention include the following:

1',3-diethylthia-2'-cyanine chloride 1,1'-diethyl-2,2-cyanine chloride 3,3-diethyloxacarbocyanine iodide 5,5'-dichloro-3,3'-diethylthiacarbocyanine iodide 1,1-diethyl-Z,2'-carbocyanine iodide 3,3'-diethylthiazolocarbocyanine iodide 3,3'-diethyl-4,4'-diphenylthiazolocarbocyanine iodide 3,3-diethyl-9-methylthiacarbocyanine iodide 1,3,3-triethylbenzimidazole-oxacarbocyanine iodide -chloro-1,3,3-triethylbenzimidazolo-oxacarbocyanine iodide 5,6-dichloro-l,3,3-triethylbenzimidazolothiacarbocyanine iodide 1, l'-3 -triethylbenzimidazolo-2'-carbocyanine iodide 1,1',3-triethylbenzimidazolo-4-carbocyanine iodide, l,l-diethyl-2,4-carbocyanine iodide 1',3-diethyl-4-methylthiaZolo-2'-carbocyanine iodide 3,3-diethylthiadicarbocyanine iodide 1, l '-diethyl-2,2'-dicarbocyanine iodide 1',3-diethylthia-2'-dicarbocy-anine iodide Anhydro-S,5',6,6-tetrachloro-1,1,3-triethyl-3'-(4-sulfobutyl)-benzimidaz0locarbocyanine hydroxide Anhydro5,6-dichloro-1-ethyl-3-(3-sulfobutyl)-3'-(3- sulfopropyl -4',5'-benzobenzimidazolothiacarbocyanine hydroxide 1,1',3 ,3 '-tetraethyl-naphth[ 1,2-d] imidazolocarbocyanine iodide Anhydro-S,6-dichloro-l,3-diethyl-(3-sulfobu'tyl) benzimidazoloselenacarbocyanine hydroxide 1,Z-diethylthia-4'-carbocyanine iodide Anhydro-S,5',6,6'-tetrachloro-1,l'-diethyl-3,3'-di(4- sulfobutyl) benzimidazolocarbocyanine hydroxide.

Typical hemicyanine dyes (including p dialkylaminostyryl dyes) which may be protonated and employed in the processes and solutions of the invention have the following general formula:

wherein R X, Z L, d and m have the meanings given above; and, R and R each represents a substituent selected from the group consisting of hydrogen, an alcohol radical, e.g., an alkyl substituent (including substituted alkyl) of from 1 to 18, and preferably 1 to 8 carbon atoms, including the specific substituents given for R and R above, or an aryl substituent such as phenyl and naphthyl, or R and R taken together represent the atoms required to form a ring, such as a heterocyclic nucleus having 5 to 6 atoms, e.g., piperidine, morpholine or pyrrolidine. Some. specific hemicyanine dyes which can be protonated and employed in this invention include the p-dialkylaminostyryl dyes such as 2-p-dimethylaminostyrylbenzothiazole ethiodide; l-methyl-2 p dimethylaminostyryl pyridinium iodide; B-methyl-Z-p-dimethylaminostyryl thiazolinium iodide; 3,5 -dimethyl 4 phenyl- Z-pdimethylarninostyrylthiazolinium iodide; and, the dye having the following structural formula:

Protonation of dyes containing the amidinium ion auxochrornophore system can be effected in any convenient manner, such as reaction of the dye with any acid of sufiicient strength to protonate the dye, and which does not adversely affect the dye. Acids which protonate dyes having the amidinium ion auxochromophore system include, for example, sulfuric, sulfonic, phosphoric, and phosphonic acids. The most convenient method for pr! tonation is to dissolve the dye in an aqueous solution containing sufficient acid to protonate the dye. The strength of the acidic solution will depend, of course, on the particular dye being protonated. PH of 1 to 4 is preferred.

When a dye having the amidinium ion auxochromo phore system is protonated, the characteristic resonance is destroyed and the compound becomes colorless. The protonated form of these dyes are vastly more soluble in water (and other polar solvents) than the unprotonated form. When the protonated form of dyes having the amidinium ion auxochromophore system are added to emulsions or colloids of sufl'lciently high pH, the dye is regenerated in its unprotonated form, and spectrally sensitizes the silver halide grains. Silver halide emulsions having a pH in excess of about 4 will generally convert the protonated form of the dye to its unprotonated form. Emulsions usually have a pH on the order of about 5.5 to 7. Emulsions having a pH in this range, or a higher pH, convert the protonated dyes to their unprotonated form. In some instances, it is desirable to adjust the pH of the emulsion after addition of the aqueous solution of protonated dye thereto. The pH of the emulsion can be conveniently regulated, for example by addition of a suitable base, e.g., sodium hydroxide.

In the embodiment of the invention described above, where the protonated dye is dispersed in a hydrophilic colloid, the colloid itself may have a suificiently high pH to convert the dye to its unprotonated form. It is possible, however, to use colloids having a sufliciently low pH that the dye remains therein in its protonated form, and is not converted to its protonated form until added to a photographic silver halide emulsion.

Typical hydrophilic colloids in which the protonated dye is dispersed, and typical hydrophilic colloids which can be used as binder for the silver halide, include gelatin, polyvinyl alcohol and the other colloids (or dispersing agents) disclosed and referred to in Beavers U.S. Patent 3,039,873 (issued June 19, 1962), column 13.

It is sometimes convenient to dissolve more than one protonated dye containing the amidinium ion auxochromophore system in an aqueous solution, and add this combination of dyes in solution to a silver halide emulsion (or first to a hydrophilic colloid and then to the silver halide emulsion as described above). This procedure may be used for supersensitization purposes, or a combination of dyes may be used to obtain the desired range of spectral sensitization.

Emulsion spectrally sensitized in accordance with this invention may contain other spectral sensitizing dyes which do not have the amidinium ion auxochromophore system, e.g., merocyanine dyes. The emulsion can also contain various supersensitizers for the dyes added to the emulsion in accordance with the invention. Supersensitization can be accomplished in such emulsion with the same materials, and using the same techniques, as disclosed in the prior art.

Photographic silver halide emulsions spectrally sensitized in accordance with this invention may contain any of the usual addenda, such as speed increasing compounds, hardeners, antifoggants, color-formers etc.

The processes and solutions of the invention are effective in sensitizing any of the light sensitive silver halides, such as silver chloride, silver bromide, silver iodide and mixed halides such as silver chlorobromide, silver bromoiodide and silver chlorobromoiodide. The concentration of dye required to spectrally sensitize the emulsion varies with the particular dye used and the effects desired. Generally, concentrations of dye in the range of about 5 to about 100 mg. per liter of flowable emulsion (or from 0.01 to 1 g. dye per mole of silver halide) gives good spectral sensitization.

This invention will be further illustrated by the following examples.

Example 1 A spectral sensitizing dye having the amidinium ion auxochromophore system anhydro 5,5,6' tetrachlorol,1,3 triethyl 3' (4-sulfobutyl)-benzimidazolocarbocyanine hydroxide was protonated by dissolving 30 mg. of the dye in 1.0 ml. of 2.0 N sulfuric acid, and brought up to a total of 30 ml. with distilled water. The protonated form of the dye is soluble in water, colorless and may be represented by the following structure:

(CI-I2): SO36 The unprotonated form of this dye, which is colored and insoluble in water, has the following formula:

Et at r'r N or o1 G=CHCH=CHC I 01- 01 a t El (C1194 A gelatin silver chlorobromide emulsion (pH) was sensitized with the aqueous solution of protonated dye prepared as described above. A control was sensitized with a methanol solution of the unprotonated form of the dye in the conventional manner. The dye in both cases was added to the liquid emulsion at a concentration of 225 mg. dye per mole of silver, and the emulsion was coated on a cellulose acetate support at 175 mg. silver per square foot and 175 mg. gelatin per square foot. The coatings were exposed on a sensitometer, developed for 2 /2 minutes in Kodak developer D-l9, fixed, washed and dried. The relative speed and the percent maximum absorption (at 580 m were essentially the same. However, the control coating showed defects (bare spots) due to the use of methanol therein. There were no coating defects using the protonated dye in accordance with the invention. In another example, the emulsions also contained an oxacarbocyanine spectral sensitizer of the type described in Belgian Patent 659,853 at a concentration of mg. per mole of silver. The relative speed and percent maximum absorption were essentially the same with each coating. Again, the control coating showed defects due to the presence of methanol therein, whereas the coating prepared with protonated dye in accordance with the invention was free from coating defects.

Example 2 The dye, anhydro 5,5,6,6'-tetrachloro-1,1'-diethyl-3,3'- di (4-sulfobutyl)-benzimidazolocarbocyanine hydroxide, is protonated in the same manner as in Example 1 but using 0.25 ml. of 2.0 N sulfuric acid. An emulsion is sensitized, coated and tested as in Example 1, a control being made with a methanolic solution with the unprotonated form of the dye as in Example 1. The results obtained with the test and control coatings with respect to coating properties and percent maximum absorption (at 570 m are similar to those of the test and control coatings in Example 1. However, the coating sensitized using the protonated form of the dye shows an unexpected increase of about 25% in relative speed. Good results, similar to those obtained in Example 1, are obtained when the emulsion also contains 160 mg. per mole of silver of an oxacarbocyanine spectral sensitizer of the type described in Belgian Patent 659,853.

Examples 3-12 Good coating and spectral sensitization, similar to the results obtained with the test coating in Example 1, are obtained when the following dyes are protonated, added to an emulsion and tested as in Example 1:

1',3-diethylthia-2-cyanine chloride 1, 1'-diethyl-2,2'-cyanine chloride 3,3-diethyloxacarbocyanine iodide 5,5'-dichloro-3,3'-diethylthiacarbocy-anine iodide 3 ,3 -diethylthiazolocarbocyanine iodide 1,3,3'-triethylbenzimidazolo-oxacarbocyanine iodide 5,6-dichloro-l,3,3-triethylbenzimidazolothiacarbocyanine iodide 1,1'-diethyl-2,4-carbocyanine iodide 1,3-diethylthia-2'-dicarbocyanine iodide 2-p-dimethylaminostyrylbenzothiazole ethiodide.

Example 13 The procedure of Example 1 is followed except that the aqueous solution of protonated dye is dispersed in an aqueous gelatin solution having a pH of about 6. The protonated dye is converted to its colored, unprotonated form. The mixture is homogenized and dried. The dispersion of dye in gelatin is then added to a liquid silver halide emulsion as in Example 1, and results similar to the test coating in Example 1 are obtained with respect to coating properties and spectral sensitization.

The novel, stable dye solutions of this invention are useful in spectrally sensitizing photographic silver halide emulsions and for spectrally sensitizing other forms of silver halide, such as binderless deposits of silver halide on a support, e.g., evaporated silver halide films, by bathing such films in the novel solutions of the invention after the pH of the solution is raised to convert the dye to its unprotonated form.

Photographic emulsions and materials spectrally sensitized in accordance with the method of this invention may be used in any products in which conventionally sensitized silver halide emulsions are employed, such as reversal films, direct positive films, emulsions having color couplers, dye bleach photographic elements and the like.

The invention has been described in detail with particular reference to preferred embodiments thereof, but, it will be understood that variations and modifications can be effected within the spirit and scope of the invention described hereinabove and in the appended claims.

I claim:

1. The method of spectrally sensitizing photographic silver halide grains dispersed in an alkali-permeable colloid which comprises:

(1) protonating a photographic spectral sensitizing dye having the following formula:

wherein Z and Z each represents the atoms required to complete a nucleus selected from the group con sisting of a thiazole nucleus, a benzothiazole nucleus, an oc-IlflPhihOthliZOlG nucleus, a ,B-naphthothiazole nucleus, a benzoxazole nucleus, a l-alkyl imidazole nucleus, 21 l-aryl imidazole nucleus, a l-alkyl benzirnidazole nucleus, a l-aryl benzimidazole nucleus, a 1-alky1naphth[1,2-d]imidazole nucleus, a l-arylnaphth[l,2-d]imidazole nucleus, a selenazole nucleus and a benzoselenazole nucleus; R and R each represents an alkyl substituent; L represents a methine group; m represents an integer of from 1 to 3; and, X represents an acid anion; and,

(2) adding an aqueous solution of the protonated dye to a fluid dispersion of light sensitive silver halide grains in alkali-permeable colloid, said dispersion having a pH sufiiciently high to convert the protonated dye to its unprotonated, colored form, thereby spectrally sensitizing said silver halide grains.

2. The method of spectrally sensitizing photographlc silver halide grains dispersed in an alkali-permeable colloid which comprises:

(1) protonating a photographic spectral sensitizing dye having the following formula:

wherein Z and Z each represents the atoms required to complete a nucleus selected from the group consisting of a thiazole nucleus, a benzothiazole nucleus, an a-naphthothiazole nucleus, a fi-naphthothlazole nucleus, a benzoxazole nucleus, a l-alkyl imidazole nucleus, a l-aryl imidazole nucleus, a l-alkyl benzimidazole nucleus, a l-aryl benzimidazole nucleus, a l-alkylnaphth[l,2-d]imidazole nucleus, a l-arylnaphth[1,2-d]imidazole nucleus, a selenazole nucleus and a benzoselenazole nucleus, at least one of Z and Z being selected from the group consisting of a l-alkylbenzirnidazole nucleus and a 1-alkylnaphth[1, 2-d]imidazole nucleus; R and R each represents an alkyl substituent containing from 1 to 4 carbon atoms; L represents a methine group; in represents an integer of from 1 to 3; and X represents an acid anion; and,

(2) adding an aqueous solution of the protonated dye to a fluid dispersion of light sensitive silver halide grains in alkali-permeable colloid, said dispersion having a pH sutficiently high to convert the protonated dye to its unprotonated, colored form, thereby spectrally sensitizing said silver halide grains.

3. The method of spectrally sensitizing photographic silver halide grains dispersed in an alkalipermeable colloid which comprises:

(1) protonating a photographic spectral sensitizing dye having the formula:

wherein Z and Z each represents the atoms required to complete a l-alkyl benzimidazole nucleus; R and R each represents an alkyl substituent containing from 1 to 4 carbon atoms; L represents a methine group; and X represents an acid anion; and,

(2) adding an aqueous solution of the protonated dye to a fluid dispersion of light sensitive silver halide grains in alkali-permeable colloid, said dispersion having a pH sulficiently high to convert the protonated dye to its unprotonated, colored form, thereby spectrally sensitizing said silver halide grains.

4. The method of spectrally sensitizing photographic silver halide grains dispersed in an alkali-permeable colloid which comprises:

(1) protonating a photographic spectral sensitizing dye having the following general formula:

wherein d represents an integer of from 1 to 2; m represents an integer of from 1 to 3; L represents a methine group; R and R each represents a substituent selected from the group consisting of hydrogen, an alcohol radical, an aryl substituent, and taken together, the atoms required to complete a heterocyclic nucleus; R represents an alcohol radical; Z represents the atoms required to complete a nucleus selected from the group consisting of a thiazole nucleus, a benzothiazole nucleus, an u-naphthothiazole nucleus, a fi-naphthothiazole nucleus, a benzoxazole nucleus, a l-alkyl imidazole nucleus, a l-aryl imidazole nucleus, a 1-alky1naphtha[l,2-d]irnidazole nucleus, a 1-arylnaphth[l,2-d]imidazole nucleus, a selenazole nucleus and a benzoselenazole nucleus; and X represents an acid anion; and,

(2) adding an aqueous solution of the protonated dye to a fluid dispersion of light sensitive silver halide grains in alkali-permeable colloid, said dispersion having a pH sufliciently high to convert the protonated dye to its unprotonated, colored form, thereby spectrally sensitizing said silver halide grains.

5. A method of spectrally sensitizing photographic silver halide grains dispersed in an alkali-permeable colloid which comprises:

(1) protonating a photographic spectral sensitizing dye having the following structural formula:

wherein Z and Z each represents the atoms required to complete a nucleus selected from the group consisting of a thiazole nucleus, a benzothiazole nucleus, an :x-naphthothiazole nucleus, a B-naphthothiazole nucleus, a benzoxazole nucleus, a l-alkyl imidazole nucleus, a l-aryl imidazole nucleus, a l-alkyl benzimidazole nucleus, a l-aryl benzimidazole nucleus, a l-alkylnaphth[1,2-d]imidazole nucleus, a l-arylnaphth[l,2-d]imidazole nucleus, a selenazole nucleus and a benzoselenazole nucleus; R and R each repre' sents an alkyl substituent; L represents a methine group; In represents an integer of from 1 to 3; and X represents an acid anion;

(2) adding an aqueous solution of said protonated dye to a fluid hydrophilic colloid; and,

(3) adding the mixture of dye and hydrophilic colloid to a fluid dispersion of light sensitive silver halide grains in alkali-permeable colloid to spectrally sensitize the silver halide, at least one of said hydrophilic colloid and said dispersion having a pH sufiiciently high to convert the protonated dye to its unprotonated, colored form.

6. A method for spectrally sensitizing photographic silver halide grains dispersed in an alkali-permeable colloid which comprises:

(1) protonating a photographic spectral sensitizing dye having the following structural formula:

.-z rZ1\ wherein Z and Z each represents the atoms required to complete a nucleus selected from the group consisting of a thiazole nucleus, a benzothiazole nucleus, an a-naphthothiazole nucleus, a ,B-naphthothiazole nucleus, a benzoxazole nucleus, a l-alkyl imidazole nucleus, a l-aryl imidazole nucleus, a l-alkyl benzimidazole nucleus, 21 l-aryl benzimidazole nucleus, a 1-alkylnaphth[1,2-d]imida- 'zole nucleus, a 1-arylnaphth[l,2-d]imidazole nucleus, a selenazole nucleus and benzoselenazole nucleus, at least one of Z and Z being selected from the group consisting of a l-alkylbenzimidazole nucleus and a l-alkylnaphth[l,2-d]imidazole nucleus; R and R each represents an alkyl substituent containing from 1 to 4 carbon atoms; L represents a methine group; m represents an integer of from 1 to 3; and, X represents an acid anion;

(2) adding an aqueous solution of said protonated dye to a fluid hydrophilic colloid; and,

(3) adding the mixture of dye and hydrophilic colloid to a fluid dispersion of light sensitive silver halide grains in alkali-permeable colloid to spectrally sensitize the silver halide, at least one of said hydrophilic colloid and said dispersion having a pH sufliciently high to convert the protonated dye to its unprotonated, colored form.

7. The method of spectrally sensitizing silver halide grains as defined in claim 5 wherein said Z and Z represents the atoms required to complete a l-alkylbenzimidazole nucleus.

8. The method of providing spectrally sensitized photographic silver halide emulsion coatings which comprises:

(1) dissolving a photographic spectral sensitizing dye in an aqueous solution which is substantially free from organic solvent and which has a pH sufiiciently low to protonate the dye, said dye having the following formula:

herein Z and Z each represents the atoms required to complete a nucleus selected from the group consisting of a thiazole nucleus, a benzothiazole nucleus an a-naphthothiazole nucleus, 9. .[i-naphthothiazole nucleus, a benzoxazole nucleus, a l-alkyl imidazole nucleus, a l-aryl imidazole nucleus, a l-alkyl benzimidazole nucleus, :1 l-aryl benzimidazole nucleus, a l-alkylnaphth[1,2-d]imidazole nucleus, a 1-arylnaphth[l,2-d]imidazole nucleus, a selenazole nucleus and benzoselenazole nucleus; R and R each represents an alkyl substituent; L represents a methine group; in represents an integer of from l to 3; and X represents an acid anion;

(2) adding said aqueous solution of protonated dye to a fluid dispersion of light sensitive silver halide grains dispersed in alkali-permeable colloid, said dispersion being substantially free from organic solvent and having a pH sufliciently high to con- -vert the protonated dye to its unprotonated, colored form, therby spectrally sensitizing the silver halide; and,

(3) coating the spectrally sensitized fluid silver halide emulsion, substantially in the absence of organic solvent, onto a support.

9. The method of providing spectrally sensitized photographed silver halide emulsion coatings as defined in claim 8 wherein at least one of said Z and said Z represents the atoms required to complete a l-alkylbenzimidazole nucleus or a 1-alkylnaphth[1,2-d]imidazole nucleus.

10. The method of providing spectrally sensitized photographic silver halide emulsion coatings as defined in claim 8 wherein said Z and said Z each represents the atoms required to complete a l-alkylbenzirnidazole nucleus.

11. The method of providing spectrally sensitized photographic silver halide coatings which comprises:

(1) dissolving a photographic spectral sensitizing dye in an aqueous acidic solution having a pH sufliciently low to protonate the dye, said solution being substantially free from organic solvent, and said dye having the following formula:

wherein Z and Z each represents the atoms required to complete a nucleus selected from the group consisting of a thiazole nucleus, a benzothiazole nucleus, an a-naphthothiazole nucleus, a fi-naphthothiazole nucleus, a benzoxazole nucleus, a l-alkyl imidazole nucleus, 21 l-aryl imidazole nucleus, a l-alkyl benzimidazole nucleus, a l-aryl benzimidazole nucleus, a l-alkylnaphth[1,2-d]imidazole nucleus, a l-arylnaphth[1,2-d]imidazole nucleus, a selenazole nucleus and benzoselenazole nucleus, at least one of Z and Z being selected from the group consisting of a l-alkyl-benzimidazole nucleus and l-alkylnaphth [l,2-d]imidazole nucleus; R and R each represents an alkyl substituent containing from 1 to 4 carbon atoms; L represents a methine group; m represents an integer of from 1 to 3; and, X represents an acid anion;

(2) adding said aqueous solution of protonated dye to a hydrophilic colloid substantially free from organic solvent;

(3) adding the mixture of dye hydrophilic colloid to a fluid dispersion of light sensitive photographic silver halide grains dispersed in alkali-permeable colloid which is substantially free from organic solvent, to spectrally sensitize the silver halide, at least one of said hydrophilic colloid and said alkalipermeable colloid have a pH sufficiently high to convert the protonated dye to its unprotonated, colored form; and,

(3) coating said spectrally sensitized, fluid silver halide emulsion, substantially in the absence of organic solvent, onto a support.

12. The method of providing spectrally sensitized photographic silver halide emulsion coatings which comprises:

(1) dissolving a photographic spectral sensitizing dye having the amidinium ion auxochromophore system in an aqueous solution having a pH from about 1 to 4, said aqueous solution being substantially free from 11 organic solvent, and said dye having the following formula:

I' r R1l I--( 3=L-L=L-=NR:

wherein Z and Z each represents the atoms required to complete a l-alkyl benzimidazole nucleus; R and R each represents an alkyl substituent containing from 1 to 4 carbon atoms; L represents a methine group; and, X represents an acid anion;

(2) adding said aqueous solution of protonated dye to a fluid dispersion of light sensitive silver halide grains dispersed in alkali-permeable colloid, said dispersion being substantially free from organic solvent and having a pH from about 5.5 to 7.0, thereby spectrally sensitizing the silver halide; and,

(3) coating the spectrally sensitized fluid silver halide emulsion, substantially in the absence of organic solvent, onto a support.

13. The method of providing spectrally sensitized photographic silver halide coatings which comprises:

(1) dissolving a photographic spectral sensitizing dye having the arnidiniurn ion auxochromophore system in an aqueous acidic solution having a pH from about 1 to 4, said solution being substantially free from organic solvent, and said dye having the follow ing general formula:

-z e. RiNC=LL=LO=-N-Rz wherein Z and Z each represents the atoms required to complete a l-alkyl benzimidazole nucleus; R and R each represents an alkyl substituent containing from 1 to 4 carbon atoms; L represents a methine group; and, X represents an acid anion;

(2) adding said aqueous solution of protonated dye to a hydrophilic colloid substantially free from organic solvent;

(3) adding the mixture of dye in hydrophilic colloid to a fluid dispersion of light sensitive photographic silver halide grains dispersed in alkali-permeable colloid which is substantially free from organic solvent, to spectrally sensitize the silver halide, at least one of said hydrophilic colloid and said alkali-permeable colloid having a pH from about 5.5 to 7.0; and,

(4) coating said spectrally sensitized, fluid silver halide emulsion, substantially in the absence of organic solvent, onto a support.

14. The method of spectrally sensitizing a photographic gelatin silver halide emulsion which comprises protonating anhydro 5,5',6,6-tetrachloro-l,l'-diethyl3,3'-di-(4- sulfobutyl)benzimidazolocarbocyanine hydroxide by dissolving said dye in an aqueous solution of sulfuric acid; and, adding said solution of protonated dye to a photographic gelatin silver halide emulsion having a pH of at least 6.0 whereby said protonated dye is converted to its unprotonated, colored form, and the silver halide is spectrally sensitized.

References Cited Sheppard et al., Journal Physical Chemistry, vol. 32, pp. 751-762, 1923 I. TRAVIS BROWN, Primary Examiner US. Cl. X.R. 

